Introduction of z/OS Basics Chapter 5: Working with data sets © 2006 IBM Corporation
Chapter 05 Working with Datasets Chapter objectives § Be able to: § Explain what a data set is § Describe data set naming conventions and record formats § List some access methods for managing data and programs § Explain what catalogs and VTOCs are used for § Be able to create, delete, and modify data sets 2 © 2006 IBM Corporation
Chapter 05 Working with Datasets Key terms in this chapter § § block size catalog data set high level qualifier (HLQ) § library § logical record length (LRECL) 3 § § member PDS and PDSE record format (RECFM) system managed storage (SMS) § virtual storage access method (VSAM) § VTOC © 2006 IBM Corporation
Chapter 05 Working with Datasets What is a data set? § A data set is a collection of logically related data records stored on one disk storage volume or a set of volumes. § A data set can be: – a source program – a library of macros – a file of data records used by a processing program. § You can print a data set or display it on a terminal. The logical record is the basic unit of information used by a program running on z/OS. 4 © 2006 IBM Corporation
Chapter 05 Working with Datasets Dataset Naming 5 © 2006 IBM Corporation
Chapter 05 Working with Datasets What an access method is § Defines the technique used to store and retrieve data. § Includes system-provided programs and utilities to define and process data sets. § Commonly used access methods include the following: – VSAM, QSAM, BDAM, and BPAM. 6 © 2006 IBM Corporation
Chapter 05 Working with Datasets DASD: Use and terminology § Direct Access Storage Device (DASD) is another name for a disk drive. § DASD volumes are used for storing data and executable programs. § Data sets in a z/OS system are organized on DASD volumes. – A disk drive contains cylinders – Cylinders contain tracks – Tracks contain data records. 7 © 2006 IBM Corporation
Chapter 05 Working with Datasets 8 © 2006 IBM Corporation
Chapter 05 Working with Datasets Using a data set § To use a data set, you first allocate it. Then, access the data using macros for the access method that you have chosen. § Various ways to allocate a data set: – ISPF data set panel, option 3. 2 – Access Method Services – TSO ALLOCATE command – job control language (JCL) 9 © 2006 IBM Corporation
Chapter 05 Working with Datasets Allocating space on DASD volumes § How space is specified: – explicitly (SPACE parameter) – implicitly (SMS data class) § Logical records and blocks: – Smallest amount of data to be processed – Grouped in physical records named blocks § Data set extents: – Space for a disk data set is assigned in extents 10 © 2006 IBM Corporation
Chapter 05 Working with Datasets Data set record formats F record Fixed records. FB block record record Fixed blocked records. BLKSIZE = n * LRECL V record Variable records. RDW block VB BDW U record block record record Variable blocked records. BLKSIZE >= 4 + n * largest LRECL record Undefined records. No defined internal structure for access method. Record and block descriptors words are each 4 bytes long 11 © 2006 IBM Corporation
Chapter 05 Working with Datasets Types of data sets § We discuss three types in this class: – Sequential, partitioned, and VSAM § A sequential data set is a collection of records written and read in sequential order from beginning to end. § A partitioned data set (PDS) is a collection of sequential data sets, called members. – Consists of a directory and one or more members. – Also called a library. § A PDSE is a partitioned data set extended. 12 © 2006 IBM Corporation
Chapter 05 Working with Datasets Types of Non-VSAM datasets 13 © 2006 IBM Corporation
Chapter 05 Working with Datasets PDS versus PDSE § PDS data sets: – Simple and efficient way to organize related groups of sequential files. § PDSE data sets: – Similar to a PDS, but advantages include: • Space reclaimed automatically when a member is deleted • Flexible size • Can be shared • Faster directory searches 14 © 2006 IBM Corporation
Chapter 05 Working with Datasets What is a data set, and how is it stored 15 © 2006 IBM Corporation
Chapter 05 Working with Datasets How data is stored in a z/OS system § Data is stored on a direct access storage device (DASD), magnetic tape volume, or optical media. § You can store and retrieve records either directly or sequentially. § You use DASD volumes for storing data and executable programs, including the operating system itself, and for temporary working storage. § You can use one DASD volume for many different data sets, and reallocate or reuse space on the volume. 16 © 2006 IBM Corporation
Chapter 05 Working with Datasets General Dataset Specifications 17 © 2006 IBM Corporation
Chapter 05 Working with Datasets Allocating a Dataset in ISPF 18 © 2006 IBM Corporation
Chapter 05 Working with Datasets How data sets are named § Data set naming convention – Unique name • Maximum 44 characters – Maximum of 22 name segments: level qualifier • The first name in the left: high level qualifier (HLQ) • The last name in the right: low level qualifier (LLQ) • Level qualifiers are separated by '. ' – Each level qualifier: • From 1 up to 8 characters • The first must be alphabetical (A-Z) or special (@ # $) • The 7 remaining: alphabetical, national, numeric (09) or hyphen (-) • Upper case only – Example: MYID. JCL. FILE 2 HLQ: MYID 3 qualifiers 19 § Member name of partitioned data set © 2006 IBM Corporation
Chapter 05 Working with Datasets Catalogs and VTOCs § z/OS uses a catalog and a volume table of contents (VTOC) on each DASD volume to manage the storage and placement of data sets. § VTOC: – Lists the data sets on a volume – Lists the free space on the volume. 20 © 2006 IBM Corporation
Chapter 05 Working with Datasets Volume Table of Contents 21 © 2006 IBM Corporation
Chapter 05 Working with Datasets VTOC 22 © 2006 IBM Corporation
Chapter 05 Working with Datasets How a catalog is used § A catalog associates a data set with the volume on which the data set is located. § Locating a data set requires: – Data set name – Volume name – Unit (volume device type) § Typical z/OS system includes a master catalog and numerous user catalogs. 23 © 2006 IBM Corporation
Chapter 05 Working with Datasets Catalog Structure 24 © 2006 IBM Corporation
Chapter 05 Working with Datasets Locating a dataset in MVS 25 © 2006 IBM Corporation
Chapter 05 Working with Datasets Catalog and Uncataloged Datasets Note the ‘ // ‘ and parm statements used for Job Control Language 26 © 2006 IBM Corporation
Chapter 05 Working with Datasets Dataset Control Blocks (DSCB) 27 © 2006 IBM Corporation
Chapter 05 Working with Datasets VTOC Index Structure ISPF option 3. 4 28 © 2006 IBM Corporation
Chapter 05 Working with Datasets Traditional Disk Capacity (DASD) 29 © 2006 IBM Corporation
Chapter 05 Working with Datasets Large Volume (own device type) 30 © 2006 IBM Corporation
Chapter 05 Working with Datasets Data management in z/OS § Data management involves all of the following tasks: – allocation, placement, monitoring, migration, backup, recall, recovery, and deletion. § Storage management is done either manually or through automated processes (or through a combination or both). § In z/OS, DFSMS is used to automate storage management for data sets. 31 © 2006 IBM Corporation
Chapter 05 Working with Datasets Data Facility Subsystem Managed Storage (DFSMS) 32 © 2006 IBM Corporation
Chapter 05 Working with Datasets VSAM § VSAM is Virtual Storage Access Method § VSAM provides more complex functions than other disk access methods § VSAM record formats: – Key Sequence Data Set (KSDS) – Entry Sequence Data Set (ESDS) – Relative Record Data Set (RRDS) – Linear Data Set (LDS) 33 © 2006 IBM Corporation
Chapter 05 Working with Datasets VSAM Access Method 34 © 2006 IBM Corporation
Chapter 05 Working with Datasets Simple VSAM control interval 35 © 2006 IBM Corporation
Chapter 05 Working with Datasets VSAM Index Structure 36 © 2006 IBM Corporation
Chapter 05 Working with Datasets VSAM Keyed Dataset 37 © 2006 IBM Corporation
Chapter 05 Working with Datasets VSAM Sequential Dataset = ESDS 38 © 2006 IBM Corporation
Chapter 05 Working with Datasets VSAM - RRDS 39 © 2006 IBM Corporation
Chapter 05 Working with Datasets VSAM LDS 40 © 2006 IBM Corporation
Chapter 05 Working with Datasets Basic Parms for VSAM dataset 41 © 2006 IBM Corporation
Chapter 05 Working with Datasets z/OS UNIX file systems § z/OS UNIX System Services (z/OS UNIX) allows z/OS to access UNIX files. § A z/OS UNIX file system is hierarchical and byteoriented. § Files in the UNIX file system are sequential files and are accessed as byte streams. § UNIX files and traditional z/OS data sets can reside on the same DASD volume. 42 © 2006 IBM Corporation
Chapter 05 Working with Datasets MVS and File Systems 43 © 2006 IBM Corporation
Chapter 05 Working with Datasets UNIX file system structure 44 © 2006 IBM Corporation
Chapter 05 Working with Datasets Organization of the File System 45 © 2006 IBM Corporation
Chapter 05 Working with Datasets Comparison of MVS Datasets and UNIX HFS 46 © 2006 IBM Corporation
Chapter 05 Working with Datasets File System Attributes 47 © 2006 IBM Corporation
Chapter 05 Working with Datasets Summary § A data set is a collection of logically related data (programs or files) § Data sets are stored on disk drives (DASD) and tape. § Most z/OS data processing is record-oriented. Byte stream files are not present in traditional processing, except in z/OS UNIX. § z/OS records follow well-defined formats, based on record format (RECFM), logical record length (LRECL), and the maximum block size (BLKSIZE). § z/OS data set names have up to 44 characters, divided by periods into qualifiers. 48 © 2006 IBM Corporation
Chapter 05 Working with Datasets Summary (continued) § Catalogs are used to locate data sets. § VSAM is an access method that provides more complex functions than other disk access methods. § z/OS libraries are known as partitioned data sets (PDS or PDSE) and contain members. § A file in the hierarchical file system can be either a text file or a binary file. § z/OS treats an entire UNIX file system hierarchy as a collection of “data sets. ” Each data set is a mountable file system. 49 © 2006 IBM Corporation
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